Detection of walking in measurements of the movement of a user

Abstract

There is provided a method of processing measurements of acceleration to identify steps by a user, the method comprising obtaining measurements of acceleration from a device worn or carried by a user; analysing the measurements of acceleration to determine a value for a threshold that is to be used to identify steps by the user in measurements of acceleration; and using the determined value for the threshold to identify steps by the user in measurements of acceleration.

The invention claimed is: 
     
       1. A method of processing measurements of acceleration to identify steps by a user, the method comprising:
 measuring, with an accelerometer of an activity monitor worn or carried by a user, values of acceleration of the activity monitor, wherein the measured values provide a signal with measurements of acceleration; 
 analyzing, with a processor of the activity monitor, the measurements of acceleration to determine a value for a threshold that is to be used to identify a series steps by the user in the measurements of acceleration; 
 using, with the processor of the activity monitor, the determined value for the threshold to identify the series of steps by the user in the measurements of acceleration; 
 testing, with the processor of the activity monitor, the identified series of steps for regularity, including:
 determining a step time for each pair of consecutive steps in the series of steps based on the time between the consecutive steps; 
 determining a central step time based on an average of the determined step times; and 
 identifying the step time of a pair of consecutive steps as irregular based on the step time and a threshold amount of the central step time; 
 
 inserting, with the processor of the activity monitor, a new step by the user to the series of steps based on the step time being irregular and a step by the user being missed; and 
 removing, with the processor of the activity monitor, an existing step by the user from the series of steps based on the step time being irregular and there is a duplicated step by the user. 
 
     
     
       2. The method as claimed in  claim 1 , wherein the step of testing the identified steps for regularity comprises:
 identifying the step time as regular if the step time is within the threshold amount of the central step time. 
 
     
     
       3. The method as claimed in  claim 2 , wherein the step of testing the identified steps for regularity further comprises:
 if a step time for a particular pair of consecutive steps is not within a threshold amount of the central step time, determining the step time between one of the pair of consecutive steps and a step neighboring the other one of the pair of consecutive steps; 
 identifying the step time for the particular pair of consecutive steps as regular if the determined step time between the one of the pair of consecutive steps and the step neighboring the other one of the pair of consecutive steps is within a threshold amount of twice the central step time; and 
 otherwise identifying the step time for the particular pair of consecutive steps as irregular. 
 
     
     
       4. The method as claimed in  claim 2 , wherein the step of testing the identified steps for regularity further comprises:
 if the step time for a particular pair of consecutive steps is identified as irregular, comparing the step time to the central step time; 
 determining that a step between the pair of consecutive steps has been missed if the step time is greater than the central step time; and 
 determining that a step in the pair of consecutive steps is a duplicate if the step time is less than the central step time. 
 
     
     
       5. A method of processing measurements of acceleration to identify steps by a user, the method comprising:
 measuring, with an accelerometer of an activity monitor worn or carried by a user, values of acceleration of the activity monitor, wherein the measured values provide a signal with measurements of acceleration; 
 analyzing, with a processor of the activity monitor, the measurements of acceleration to determine a value for a threshold that is to be used to identify a series steps by the user in the measurements of acceleration; 
 using, with the processor of the activity monitor, the determined value for the threshold to identify the series of steps by the user in the measurements of acceleration; 
 testing, with the processor of the activity monitor, the identified series of steps for regularity, including:
 determining a step time for each pair of consecutive steps in the series of steps as the time between the consecutive steps; 
 for the smallest determined step time, computing a first variance as the variance of the step times for each pair of consecutive steps, computing a second variance as the variance of the step times when the first step forming the pair of steps with the smallest determined step time is omitted, and computing a third variance as the variance of the step times when the second step forming the pair of steps with the smallest determined step time is omitted; 
 determining that the first step forming the pair of steps with the smallest determined step time is a duplicate if the second variance is the smallest variance of the first variance, the second variance and the third variance; and 
 determining that the second step forming the pair of steps with the smallest determined step time is a duplicate if the third variance is the smallest variance of the first variance, the second variance and the third variance; and 
 
 removing, with the processor of the activity monitor, an existing step by the user from the series of steps if it is determined from a result of the step of testing that there is a duplicated step by the user. 
 
     
     
       6. The method as claimed in  claim 5 , further comprising:
 inserting, with the processor of the activity monitor, a new step by the user to the series of steps if it is determined from the result of the step of testing that a step by the user has been missed. 
 
     
     
       7. The method as claimed in  claim 1 , further comprising the steps of:
 identifying a first step and a last step for a walking part from the steps identified in the measurements of acceleration; and 
 repeating the steps of analyzing and using on the measurements of acceleration corresponding to the walking part to identify steps by the user. 
 
     
     
       8. The method as claimed in  claim 1 , wherein, for a walking part comprising a series of steps identified in the measurements of acceleration, the method further comprises:
 determining an activity level for the user from the measurements of acceleration corresponding to the walking part; and 
 discarding the walking part if the activity level of the user indicates that the user is not walking. 
 
     
     
       9. The method as claimed in  claim 1 , wherein, for a walking part comprising a series of steps identified in the measurements of acceleration, the method further comprises:
 determining if the walking part corresponds to the user walking up or down stairs; and 
 discarding the walking part if it is determined that the walking part corresponds to the user walking up or down stairs. 
 
     
     
       10. The method as claimed in  claim 9 , wherein the step of determining if the walking part corresponds to the user walking up or down stairs comprises:
 obtaining measurements of an air pressure from the device worn or carried by the user; and 
 processing the obtained measurements of air pressure to determine if there has been a change in height consistent with the user walking up or down stairs during the walking part. 
 
     
     
       11. A computer program product having computer readable code embodied therein, the computer readable code being configured such that, on execution by a suitable processing unit or computer, the processing unit or computer performs the method according to  claim 1 . 
     
     
       12. An apparatus for processing measurements of acceleration to identify steps by a user, the apparatus comprising:
 a processing unit configured to
 obtain measurements of acceleration from a device worn or carried by a user; 
 analyze the measurements of acceleration to determine a value for a threshold that is to be used to identify steps by the user in measurements of acceleration; 
 use the determined value for the threshold to identify a series steps by the user in the measurements of acceleration; 
 test the identified series of steps for regularity by:
 determining a step time for each pair of consecutive steps in the series of steps based on the time between the consecutive steps; 
 determining a central step time based on an average of the determined step times; and 
 identifying the step time of a pair of consecutive steps as irregular based on the step time and a threshold amount of the central step time; 
 
 insert a new step by the user to the series of steps if it is determined from a result of the testing that the step time is irregular and a step by the user has been missed; and 
 remove an existing step by the user from the series of steps if it is determined from the result of the testing that the step time is irregular and there is a duplicated step by the user. 
 
 
     
     
       13. The apparatus as claimed in  claim 12 , wherein the processing unit is further configured to evaluate a stride regularity of the series of steps. 
     
     
       14. The apparatus as claimed in  claim 12 , wherein the processing unit is further configured to:
 determine if the series of steps corresponds to the user walking up or down stairs; and 
 discard the series of steps if it is determined that the series of steps corresponds to the user walking up or down stairs. 
 
     
     
       15. A device that is to be worn or carried by a user, the device comprising:
 an accelerometer for providing measurements of acceleration; and 
 an apparatus as claimed in  claim 12 . 
 
     
     
       16. The method as claimed in  claim 5 , wherein the step of analyzing the measurements of acceleration comprises:
 determining one or more characteristics from the measurements of acceleration; and 
 determining a value for a threshold that is to be used to identify steps by the user from the one or more characteristics. 
 
     
     
       17. The method as claimed in  claim 5 , further comprising the steps of:
 identifying a first step and a last step for a walking part from the steps identified in the measurements of acceleration; 
 repeating the steps of analyzing and using on the measurements of acceleration corresponding to the walking part to identify steps by the user. 
 
     
     
       18. The method as claimed in  claim 5 , wherein, for a walking part comprising a series of steps identified in the measurements of acceleration, the method further comprises:
 determining an activity level for the user from the measurements of acceleration corresponding to the walking part; and 
 discarding the walking part if the activity level of the user indicates that the user is not walking. 
 
     
     
       19. The method as claimed in  claim 5 , wherein, for a walking part comprising a series of steps identified in the measurements of acceleration, the method further comprises:
 determining if the walking part corresponds to the user walking up or down stairs; and 
 discarding the walking part if it is determined that the walking part corresponds to the user walking up or down stairs. 
 
     
     
       20. The method as claimed in  claim 19 , wherein the step of determining if the walking part corresponds to the user walking up or down stairs comprises:
 obtaining measurements of an air pressure from the device worn or carried by the user; and 
 processing the obtained measurements of air pressure to determine if there has been a change in height consistent with the user walking up or down stairs during the walking part.